Worm gear with a gear ring nut

ABSTRACT

A worm gear for transforming a rotary motion into a reciprocating motion comprises a threaded spindle (2) which is mounted for rotation on at least one needle roller bearing (5) in a gear ring nut (22) which functions as a housing (21). A profiled gear ring (19) engages the thread of the spindle (2) at one peripheral point for axially displacing the gear ring nut (22). This gear ring (19) surrounds the threaded spindle (2) and is arranged eccentric to the spindle axis (3). Further, the gear ring (19) is surrounded by a radial rolling bearing on which the gear ring (19) is rotatably mounted in the housing (21). According to the invention, the housing (21) is composed of rotationally symmetrical sheet metal parts made by chipless deep drawing, the inner surfaces of which sheet metal parts directly comprise the outer rolling element raceways for the bearings. In this way, an easy-to-mount worm gear with a simplified structure is obtained.

FIELD OF THE INVENTION

The invention concerns a worm gear for transforming a rotary motion intoa reciprocating (linear) motion, comprising a threaded spindle which ismounted for rotation on at least one needle roller bearing in a gearring nut which functions as a housing, a profiled gear ring engaging athread of the spindle at one peripheral point for axially displacing thegear ring nut, the gear ring which surrounds the threaded spindle beingarranged eccentric to the spindle axis while being surrounded by aradial rolling bearing on which the gear ring is rotatably mounted inthe housing.

BACKGROUND OF THE INVENTION

A worm gear of this type is known from EP-PS 0 122 596 and comprises twogear rings arranged with ball bearings in a housing, the outer rings ofthe ball bearings being arranged in special rolling bearing receivingelements which surround the threaded spindle. The needle roller bearingswhich serve as radial supports for the gear ring nut likewise haveseparate outer or gear rings. This makes the structure rathercomplicated on the whole.

SUMMARY OF THE INVENTION

The object of the invention is to create an easy-to-mount worm gear witha simplified structure.

The invention achieves this object by the fact that the housing iscomposed of rotationally symmetrical sheet metal parts made by chiplessdeep drawing, the inner surfaces of which sheet metal parts directlycomprise the outer rolling element raceways for the bearings. Thehousing can therefore be assembled from hardened, drawn parts which atthe same time serve as bearing raceways. This results in a compactstructure of the worm gear which thus comprises only a few individualparts.

At its end remote from the gear ring, the housing can be configured inthe direction of the spindle axis as a pot-shaped piston. Thus, it isclosed at one end and the threaded spindle is protected from damage andpollution. Besides this, lubricant cannot be lost and thus remainsinside the gear ring nut.

The housing comprises an outer bearing ring for the needle rollerbearing of the threaded spindle and, connected thereto, an outer bearingring for the radial rolling bearing of the gear ring. The bearing ringfor the needle roller bearing and the bearing ring for the radialrolling bearing can be made together in one piece as a sheet metal partso that a particularly simple embodiment results.

The radial rolling bearing for the gear ring can be configured as a ballbearing transmitting both axial and radial forces. It is, however, alsopossible to configure the radial rolling bearing for the gear ring as aneedle roller bearing in which case the gear ring is rotatably mountedin the housing on two additional axial needle roller bearings. Such aconstruction offers the advantage of higher axial rigidity and higherbasic load ratings than obtained by using a ball bearing because needleroller bearings usually have higher load ratings and stiffness. Besidesthis, the design space requirement is smaller in the case of needleroller bearings.

The raceways for the rolling bearings of the gear ring are constituteddirectly by the surfaces of the gear ring. The gear ring can be retainedaxially in the housing by an inwardly bent edge of the housing. It ispossible to arrange two needle roller bearings for the threaded spindlein the housing, one of said two needle roller bearings being arranged oneach side of the gear ring. In this case, the housing can comprise anadditional bearing ring for the second needle roller bearing of thethreaded spindle, said additional bearing ring being axially retained onthe bent-over edge of the housing by an adjoining flange.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples of embodiment of the invention are represented in the drawingsand will be described more closely below. In the drawings

FIG. 1 is a longitudinal section through a worm gear whose gear ring ismounted in the housing on two axial needle roller bearings and oneradial needle roller bearing;

FIG. 2 is a longitudinal section through a worm gear comprising a ballbearing, the housing of the worm gear being made up of two parts;

FIG. 3 is a longitudinal section through a worm gear whose housing isformed integrally with two rolling bearing rings.

DETAILED DESCRIPTION OF THE DRAWINGS

A worm gear of the invention represented in FIG. 1 comprises a gear ringnut 1 which surrounds a threaded spindle 2 by which said gear ring nut 1is displaced in axial direction upon a rotation of the spindle 2 aboutthe spindle axis 3. The gear ring nut 1 constitutes a housing 4 in whichthe threaded spindle 2 is mounted for rotation on two needle rollerbearings 5 and 6. The housing 4 is made up of two deep drawn sheet metalparts. The larger one of these two parts comprises a pot-shaped piston 7which closes the receiving space for the threaded spindle 2 at one axialend, an outer bearing ring 8 for the needle roller bearing 5 and anouter bearing ring 9 for a radial rolling bearing configured as a needleroller bearing 10 on which a gear ring 11 is rotatably mounted in thehousing 4. At its end opposite the pot-shaped piston 7, this part of thehousing 4 ends in an edge 12 bent over from the outer bearing ring 9.

Axially next to this, there is arranged a further deep drawn sheet metalpart having a flange 13 which continues into a further bearing ring 14for the second needle roller bearing 6 of the threaded spindle 2. Thehousing 4 is held together by the fact the flange 13 which is situatedwithin the outer bearing ring 9 is retained axially by the edge 12.

The axis 15 of the gear ring 11 is parallel to the spindle axis 3. Thegear ring 11 is therefore arranged eccentrically with respect to thethreaded spindle 2 and meshes at one peripheral point with grooves ofthe outer thread of the threaded spindle 2. Since the gear ring 11 is inrolling contact with the threaded spindle 2, it is forced to rotate whenthe threaded spindle 2 rotates within the housing 4. To enable thetransmission of axial forces from the gear ring 11 to the housing 4,this worm gear comprises axial needle roller bearings 16 and 17 by whichthe gear ring 11 is axially mounted in the housing 4. These bearings arearranged directly on the two end faces of the gear ring 11 so that thegear ring 11 forms their raceways. The outer bearing surface for theneedle roller bearing 16 is constituted by a flange region 18 of thepart of the housing comprising the pot-shaped piston 7, while the outerbearing raceway for the rolling elements of the axial needle rollerbearing 17 is provided by the flange 13 of the part of the housingcomprising the additional bearing ring 14.

In the embodiments of FIGS. 2 and 3, the threaded spindle 2 is mountedonly on one needle roller bearing 5. In this case, a pressure force canbe exerted on the pot-shaped piston 7 in the direction of the spindleaxis 3 by the gear ring 19 through its radial rolling bearing which isconfigured as a ball bearing 20. The housing 21 of the gear ring nut 22of FIG. 2 comprises two deep drawn sheet metal parts, namely the partcomprising the pot-shaped piston 7 and an outer bearing ring 23 for theneedle roller bearing 5 of the threaded spindle 2, and the partcomprising the outer bearing ring 24 for the mounting of the ballbearing 20 for the gear ring 19. These two parts are joint to each otherin the region of the needle roller bearing 5 by mechanical means.

In the embodiment of FIG. 3, the housing 25 of the gear ring nut 26 ismade in one piece with the outer bearing ring 23 of the needle rollerbearing 5 and the outer bearing ring 24 of the radial rolling bearing ofthe gear ring 19. Similar to the housing 4 of FIG. 1 and the housing 21of FIG. 2, the housing 25 also comprises an inwardly bent edge 12 bywhich the gear ring 19, whose axis 15 is offset from the spindle axis 3,is retained axially within the housing.

    ______________________________________    List of Reference Numbers    ______________________________________    1               Gear ring nut    2               Threaded spindle    3               Spindle axis    4               Housing    5               Needle roller bearing    6               Needle roller bearing    7               Pot-shaped piston    8               Outer bearing ring    9               Outer bearing ring    10              Needle roller bearing    11              Gear ring    12              Bent-over edge    13              Flange    14              Bearing ring    15              Gear ring axis    16              Axial bearing    17              Axial bearing    18              Flange region    19              Gear ring    20              Ball bearing    21              Housing    22              Gear ring nut    23              Outer bearing ring    24              Outer bearing ring    25              Housing    26              Gear ring nut    ______________________________________

We claim:
 1. A worm gear for transforming a rotary motion into areciprocating (linear) motion, comprising a threaded spindle which ismounted for rotation on at least one needle roller bearing in a gearring nut which functions as a housing, a profiled gear ring engaging athread of the spindle at one peripheral point for axially displacing thegear ring nut, the gear ring which surrounds the threaded spindle beingarranged eccentric to the spindle axis while being surrounded by aradial rolling bearing on which the gear ring is rotatably mounted inthe housing, wherein the housing (4, 21, 25) is composed of rotationallysymmetrical sheet metal parts made by chipless deep drawing, said sheetmetal parts having inner surfaces which directly comprise outer rollingelement raceways for said needle roller bearing and said radial rollingbearing.
 2. A worm gear of claim 1, wherein an end of the housing (4,21, 25) remote from the gear ring (11, 19) is configured in spindledirection as a pot-shaped piston (7).
 3. A worm gear of claim 1, whereinthe housing (4, 21, 25) comprises an outer bearing ring (8, 23) formingone of the raceways for the needle roller bearing (5) of the threadedspindle (2) and, connected to said outer bearing ring (8), a furtherouter bearing ring (9, 24) forming another one of the raceways for theradial rolling bearing of the gear ring (11, 19).
 4. A worm gear ofclaim 3, wherein the bearing ring (8, 23) for the needle roller bearing(5) of the threaded spindle (2) and the bearing ring (9, 24) for theradial rolling bearing of the gear ring (11, 19) are made together inone piece as a sheet metal part.
 5. A worm gear of claim 3, wherein theradial rolling bearing for the gear ring (19) is configured as a ballbearing (20).
 6. A worm gear of claim 3, wherein the radial rollingbearing for the gear ring (11) is configured as a needle roller bearing(10), and further comprising two additional axial needle roller bearings(16, 17) for rotatably supporting the gear ring (11) in the housing (4)in axial direction, said axial needle roller bearings (16, 17) beingpositioned on opposite end faces of the gear ring.
 7. A worm gear ofclaim 6, wherein the gear ring (11, 19) has surfaces which directly forminner raceways for the rolling bearings (10, 16, 17, 20) of the gearring (11, 19).
 8. A worm gear of claim 1, wherein the gear ring (11, 19)is retained axially in the housing (4, 21, 25) by an inwardly bent edge(12) of the housing (4, 21, 25).
 9. A worm gear of claim 8, wherein twoneedle roller bearings (5, 6) for the threaded spindle (2) are arrangedin the housing (4), one of said needle roller bearings (5, 6) beingarranged on each side of the gear ring (11).
 10. A worm gear of claim 9,wherein the housing (4) comprises an additional bearing ring (14) forthe second needle roller bearing (6) of the threaded spindle (2), saidadditional bearing ring (14) being retained on the bent-over edge (12)of the housing (4) by an adjoining flange (13).